USB Audio - Strange Behavior of Explicit Feedback calculator

Sub forums for various specialist XMOS applications. e.g. USB audio, motor control and robotics.
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Joined: Fri Mar 19, 2010 4:49 am

Post by bearcat »

Apple's tech note certainly pushes the implicit feedback method.

I went ahead and implemented it as a definable. Here's my results:

1 - Windows and Theyscon driver. Theyscon uses implicit feedback not matter if set for explicit or implicit on the device. Works well. Input and output track each other +-1 sample max.

2 - iOS. Implicit feedback has issues with an iPhone at least. Tracking wonders around, and can cause a buffer "sync" (my code is +-24 samples). 48K sample rate is much better, but still not perfect. Explicit feedback is required in my testing. +-2 samples were achieved with stability.

3 - OSX. Not tested yet.

4 - Linux. Didn't work with Ubuntu V12, either implicit or explicit. Didn't explore yet.

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Joined: Sat Nov 28, 2020 6:36 pm

Post by nuel1986 »

Hi @bearcat! Have you had a chance to test implicit feedback on macOS? I'm implementing that at the moment and getting some erratic behavior (namely, the OUT endpoint takes 300-400mS to respond with the correct number of samples) so was very curious to know what your experience has been.

Thanks in advance.